Monday, March 17, 2008

Gas Piston ARs

Look another one! I'm not a huge fan of the gas piston AR/M-16/M-4. They do make the gun run cleaner. Which is nice because cleaning an AR is a pain. They are generally billed as making the gun run more reliably. This is generally bunk. Why?

AR-15s are actually very reliable. The AR has a failure rate around 1% in pretty hard conditions like the Army "dust test". Once you are that reliable, proving another rifle is better in a statistically significant sense is practically impossible. You are so far down the tail of the statistical distribution that you need a huge number of trials to differentiate between the systems in a statistically definitive way. Nobody does that many. This is why all the AR-15 sand tests come back with answers like "the current rifle is good enough."

Jamming in the AR-15 is not generally caused by gas blowing into the action. Jamming is caused by the close tolerances used in the rifles to make them accurate. AR-15s don't jam in the desert because they "shit where they eat." AR-15s jam in the desert because they are full of sand because they are in the desert. Putting a gas piston on the upper does not make them less full of sand or loosen up the parts tolerances so the sand doesn't cause problems.

The reason the military doesn't use piston uppers is not because it is a new concept. Colt tested designs like these in the 1960s. The reason the military doesn't use them is that they aren't significantly better than what we have. Reliability doesn't change much. Accuracy, on the other hand, changes a lot with piston uppers being about half as accurate as a standard AR.